Electromagnetic vibratory devices



April 1, 1969 I DAS GUPTA ET AL 3,436,568

ELECTROMAGNETIC VIBRATORY DEVICES Filed April 19, 1966 United States Patent 3,436,568 ELECTROMAGNETIC VIBRATORY DEVICES Raujit Das Gupta, Mysoredayasimha, Rau Somasekhara,

Krishnappa Sitaramarao, and Rangaiyer Yegnanarayan, Dooravani, Nagar, India, assignors to Indian Telephone Industries Limited, Dooravani, Nagar,

Bangalore, India, a company of India Filed Apr. 19, 1966, Ser. No. 543,625 Int. Cl. H02k 33/18 US. Cl. 310-25 3 Claims ABSTRACT OF THE DISCLOSURE armature is slit longitudinally to provide at least a pair of legs each extending at a fixed angle from the armature toward a respective pole piece and spaced from the permanent magnet toward the gap.

This invention relates to electromagnetic vibratory devices and more particularly to electroaooustic transducers.

The object of the invention is to propose a construction of an electromagnetic vibratory device, which is eificient, cheap in orginal costs and simple to manufacture.

In accordance with the invention, there is provided an electromagnetic vibratory device comprising two pole pieces of different polarity terminating at first ends which extend toward each other. A gap is formed between the first ends of the pole pieces, and a permanent magnet extends between the second or inner ends of the pole pieces. The device includes an A.C. coil or coils, and an armature is pivotally mounted on the base of the device between the magnet and the first ends of the pole pieces. The free end of the armature extends into the gap, and the other end of the armature is split to form bent legs extending in opposite directions toward respective pole pieces. These legs provide a low reluctance path for A.C. magnetic fluxes.

The one end of the armature is split into one or more sections to form split arms at 180 to each other, the split arms facing the pole flanges of opposite polarity. The armature is preferably suspended on its own torsion arms.

Other objects and advantages of this invention will be apparent when described with reference to the accompanying drawings wherein:

FIG. 1 is a plan view (from the rear) of the electromagnetic vibratory device.

FIG. 2 is a side elevation view of the device.

FIG. 3 is a perspective view of the split armature incorporated in said device.

FIG. 4 is a front elevation view of the magnet pole piece assembly incorporated in said device.

FIGS. 5 and 6 represent the magnetic circuit of the embodiment showing the D.C. and A.C. flux paths, respectively.

The vibrating unit of the receiver comprises pole pieces 1-1' made of any high permeability magnetic material, each of which is formed into an L-shaped bracket having a pole tip and a flanged portion 16. A magnet 2 made of high energy magnetic material is clamped between the flanged portions of the pole pieces, which are secured to base 9. A pole gap 3 is formed in between the tips of the ice pole pieces. An armature 18, as having torsion arms 4-4 6, is pivoted at 10-10, between the magnet and the free pole tips, and adjusted such that gaps 7 and 7' are approximately equal. A coil 8 is positioned between the torsion arms 4, 4' and the free pole tips so that the armature passes through the central rectangular aperture 17 of the coil and does not foul with it. While, for the preferred embodiment the coil is placed around the armature, it is also possible to get the same results by using two coils, connected in series aiding, one being placed around each of the pole pieces. The armature has an extension 11 which is connected by a pin 12 to the diaphragm 13 mounted on the base 9.

The D.C. flux path is indicated by the dotted line in FIG. 5. The D.C. flux path is completed through the N pole of the magnet 2, pole piece 1, gap 7, armature 18, gap 7', pole piece 1' and the S pole of the magnet. A second D.C. flux path is completed by the N pole, pole piece 1, gap 14, split arms 5, 5' and 6 of the armature, gap 14', pole piece 1' to the S pole. A polarising flux for the armature is thereby provided. As indicated by dotted lines in FIG. 6, an A.C. flux path is completed by the split arms of the armature, gap 14, pole piece 1, air gap 7. A second A.C. flux path is completed by armature, gap 7' pole piece 1', gap 14. It is clearly seen from the type of the preceding description that an arrangement as per the preferred embodiment produces the necessary polarising flux for efiicient operation of the device and, at the same time, A.C. fluxes are confined to high permeability materials and do not pass through the magnet, which normally has a low permeability. The armature is normally held balanced at equal distances from the pole pieces, but A.C. currents, e.g., voice currents in the coil will set up unbalanced magnetic forces between the pole pieces and armature in response to which the armature will vibrate. The A.C. fluxes due to the split and formed legs of the armature, are prevented from flowing through the magnet, but are confined to the pole pieces and the armature, thus providing an arrangement for obtaining a very high efficiency electromagnetic vibratory device.

We claim:

1. An electromagnetic vibratory device comprising, in combination, a base; a pair of relatively elongated magnetic pole pieces mounted on said base in spaced, substantially parallel relation; said pole pieces having first ends, extending toward each other and defining a pole piece gap, and second ends; a permanent magnet positioned between said second ends of said pole pieces to define, with said pole pieces, a D.C. magnetic circuit including said gap; a relatively elongated magnetic armature having a first end and a free end, said armature having a pair of torsion arms extending in opposite lateral directions therefrom; means securing said torsion arms to said base, with said first end of said armature being spaced rom said permanent magnet toward said gap and with the free end of said armature extending into said gap in spaced relation to said pole piece first ends; said pole pieces, permanent magnet and armature constituting a magnetic structure mounted on said base; and signal receiving coil means operatively associated with said magnetic structure and providing an A.C. magnetic flux therein; the first end of said armature being slit longitudinally of said armature to provide at least a pair of legs integral with said armature and each extending at a fixed angle from said armature toward a respective pole piece and spaced from said permanent magnet toward said gap, said legs vibrating as a unit with said armature about said torsion arms; said legs forming a low reluctance path for the A.C. flux including said armature, said legs, the portions of said pole pieces between said legs and said pole piece first ends,

which is shown in FIG. 3 and the split arms 5-5 and and said gap, and in shunt relation with said permanent magnet; said legs being included in a second D.C. magnetic flux circuit including said permanent magnet and the remaining portions of said pole pieces between said arms and said permanent magnet.

2. An electromagnetic vibratory device, as claimed in claim 1, wherein said legs are substantially coplanar with each other and extend substantially perpendicular to the general plane of said armature.

3. An electromagnetic vibratory device, as claimed in claim 1, in'which the first end of said armature is slit along two parallel lines to provide three legs, the two outer legs extending toward one pole piece and the inner leg extending toward the opposite pole piece, whereby secondary vibrations of said armature are avoided.

4 References Cited UNITED STATES PATENTS 2,432,424 12/ 1947 Hyland et a1.

2,454,425 11/ 1948 Bauer 31O 25 XR 2,511,114 6 1950 Lavery.

2,657,374 10/1953 Bardeen.

2,912,523 11/1959 Knowles et al 179108 0 MILTON O. HIRSHFI'ELD, Primary Examiner.

D. F. DUGGAN, Assistant Examiner. 

